This invention relates to a method and an apparatus for measuring electronic parameters of a solar cell. More specifically, this invention relates to an apparatus and a method for analyzing the short circuit current, I.sub.sc, the open circuit voltage, V.sub.oc, and plotting the IV curve of a solar cell.
As solar technology moves out of the laboratory and into full scale production and the solar cells increase in size, a method and apparatus is needed to measure the electronic parameters of a solar cell quickly and efficiently. In the past, a laser beam has been coupled with a kinescope to analyze semiconductor devices as taught by Williams et al, RCA Corporate Engineering Services, pp. 76-78 (1973), Sawyer et al, Solid State Technology, Vol. 30, No. 6, pp. 37-41 and 48 (June 1977), and Sawyer, Proceedings Of The Photovoltaics Program Semi-Annual Review, pp. 708-713, (1977).
The above techniques, although useful for analyzing integrated circuits, and the short circuit current of solar cells, are not useful for finding nonuniformities in V.sub.oc or the IV curve of solar cells.
Oroshnik et al, Sol. St. Elect., Vol. 1, pp. 46-53, Pergamon Press, (1960), teaches a method and apparatus which quantitatively estimates the resistivity changes of a semiconductor and permits the plotting of photovoltage versus position on the solar cell. However, the method does not permit the direct measurement of the V.sub.oc of a solar cell.
Chandler, Proceedings Of The Southeast Section Of The Institute Of Electrical And Electronic Engineers, Inc., pp. 281-284, April 4-6, 1977, describes a method of measuring the V.sub.oc of a cell in various portions of the solar cell. The method requires a top contact with a cross hatched geometry to make the measurements. The top contact requires special processing and provides poor resolution of the open circuit voltage.
Prior to Chandler et al, the only way to measure the V.sub.oc of a portion of a solar cell was to break the solar cell into pieces or etch away portions of the metal contacts and measure each section. The measurements resulted in the destruction of the device and therefore was not only time consuming but unrealistic when applied to production operations.
Thus, it would be highly desirable to have an apparatus and a method of measuring the IV curve of a solar cell at any position on the cell, of scanning of the V.sub.oc of the solar cell, of plotting the IV curve of the solar cell at a specific point on the cell, and of measuring the I.sub.sc of the solar cell.